A host device in which digital camera functionality is integrated includes an arrangement of one or more optical elements and image sensor. Optical zoom capabilities are available if a focal length of the arrangement of optical elements can be changed, usually through mechanical means. Digital zoom capabilities are implemented electronically and are available without the need for a change in the focal length of the arrangement of one or more optical elements.
The term “pixel”, short for “picture element”, is used herein with different meanings, depending on the context: an image sensor, a display module, or a digital representation of an image. In the context of a digital representation of an image, a pixel is the smallest element of the digital representation of the image.
An image sensor will include a pixel array comprising photosensitive material. The pixel array is an array of very fine electronic pixels arranged in horizontal rows and vertical columns. Such an image sensor, for example, a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensor, is capable of receiving and capturing radiant energy, and converting the radiant energy into electronic signals that become a virtual representation of an optical image. When digital camera functionality is described as a two-megapixel, three-megapixel or five-megapixel, this is an approximate description of the number of pixels in the image sensor's pixel array. As used herein, the term captured image refers to the image read from the pixel array, discounting any margin or border pixels. For example, a two-megapixel digital camera may produce a captured image of 1600 by 1200 pixels.
A host device in which digital camera functionality is integrated typically includes a display module to display a preview image that is derived from the captured image. Looking at the preview image may assist a user of the host device in taking a photograph using the digital camera functionality, since the preview image provides the user with visual feedback as to what the digital camera “sees”. The display module includes a pixel array, which is an array of pixels arranged in horizontal rows and vertical columns. Depending on the technology for the pixel array, the pixels may comprise photo-emitting material, or may by controllable, as in liquid crystal display (LCD) technology, to block light or permit the transmission of light in varying degrees. Other technologies for pixel arrays in display modules are known in the art. The number of pixels in a pixel array of the display module is typically smaller than the number of pixels in the captured image. For example, a display may have 320 by 240 pixels.
Digital zoom is accomplished by cropping an image to retain a center part of the image with the same aspect ratio as the original and to discard the rest of the image. The retained portion is referred to herein as the cropped image, including cases where the entire image is retained. At a digital zoom level of 1×, no cropping is performed and the entire image is retained. The cropped image is therefore identical to the image before cropping. At a digital zoom level of 2×, about one quarter of the image is retained. At a digital zoom level of 3×, about one ninth of the image is retained.
A host device in which digital camera functionality is integrated may be designed to offer two or more digital zoom levels. The host device will be designed so that input provided via at least one of its user input components results in a change in the digital zoom from one offered digital zoom level to another offered digital zoom level. The cropped image and hence the preview image will change as the digital zoom changes from one offered digital zoom level to another offered digital zoom level. A user may perceive abruptness in the preview image as the digital zoom changes from one offered digital zoom level to another.
In practice, images include noise resulting from a variety of sources. Noise in an image may appear, for example, as a speckle or a pixel in a color or shade of gray unrelated to that of its neighboring pixels. The preview image is refreshed at a refresh rate, which may be fixed or variable. For example, the refresh rate may be set to 15 times per second in bright lighting conditions and to 8 times per second in dim lighting conditions. Noise in the preview image may therefore be particularly noticeable by a user, since the noise will differ from one preview image to another, even when the preview images are all at the same offered digital zoom level.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.